The overall objectives is to determine the relation of the brain, particularly the hypothalamus, to development and growth of mammary and pituitary tumors, and to utilize this information to inhibit development and growth of mammary and pituitary tumors. Since prolactin and estrogen are the principal hormones involved in development and growth of mammary tumors, and to a large extent of pituitary tumors, and since these hormones are controlled directly (prolactin) or indirectly (estrogen) by the hypothalamus, our aim will be to experimentally alter hypothalamic function (by placing lesions or implanting hormones and drugs in the hypothalamus, by administration of drugs and hormones systemically, and by use of appropriate environmental stimuli) to inhibit or accelerate development and growth of these tumors in mice, rats and dogs. Old female rats also will be utilized since they develop spontaneous mammary and pituitary tumors, which we believe are related to functional changes in hypothalamic functions in old rats. Hopefully, some of the knowledge gained from these studies will prove to be useful for developing treatments for inhibiting the onset and/or growth of mammary and pituitary tumors in human subjects.